1. Field of the Invention
The present invention relates to a drag control system for reducing the drag of an airplane or other kinds of flying machines, and a drag estimating process, and further relates to a boundary layer control system and a boundary layer control process for reducing the drag of a moving member such as a main wing of all airplane.
2. Description of the Related Art
When a flying machine flies in the air, a great deal of energy is lost due to air drag and this causes an increase in amount of fuel consumed. In an area on the surface of the flying machine where a boundary layer is transitioned to a turbulent-flow boundary layer section, particularly due to the large Reynold""s number of the flow, the loss of energy due to the friction drag of air is of a disregardable magnitude. For this reason, the transition to the turbulent-flow boundary layer section is retarded or moved back on the surface, to reduce the friction drag by maintaining a laminar-flow boundary layer section over as long an area as possible. A laminar-flow wing is well-known as a wing type developed based on such a demand.
However, the airplane flies under a variety of different conditions of speed, atmospheric temperature, altitude, attitude and the like and hence, when a laminar-flow wing is used, it is difficult to reduce the friction drag under all flying conditions. A system is known from Japanese Patent Application Laid-open No. 10-281115, which is designed to prevent the transition and peel-off of the boundary layer to reduce the friction drag by detecting the state of air flow on the surface of an object such as a main wing of an airplane using a sensor and providing vibration to the surface of the object or by ejecting air to the surface of the object from a nozzle in accordance with the detected state of air flow.
However, the system described in the above Publication suffers from the problem that a means for providing the vibration to the surface of the object or a means for ejecting air to the surface of the object is required, resulting in an increased weight and an increased cost. Moreover, another problem is that it is difficult to effectively reduce the air drag, because a sensor only detects the state of the air flow on the surface of the object, and does not detect the air drag directly.
Further, the system described in the above Publication has the problem that it is difficult to conduct a precise control for moving the transition point rearwards as far as possible to minimize the drag, because the sensor detects premonitory symptoms of occurrence of the transition and peel-off of the boundary layer, but is not intended to monitor the movement of a transition point of the boundary layer.
Accordingly, it is a first object of the present invention to provide a drag control system for effectively reducing the drag in various motion states of the flying machine, and a drag estimating process.
It is a second object of the present invention to provide a boundary layer control system and a boundary layer control process for effectively reducing the drag in various motion states of the moving member.
To achieve the above first object, according to a first aspect and feature of the present invention, there is provided a drag control system for a flying machine, comprising a thrust estimating means for estimating the thrust of the flying machine flying in the air, a motion state detecting means for detecting the motion state of the flying machine, a drag estimating means for estimating the drag of the flying machine, based on the detected motion state and the estimated thrust, a drag varying means for varying the drag of the flying machine, an operation-amount calculating means for calculating the amount of operation of the drag varying means for minimizing the estimated drag, and an operating means for operating the drag varying means, based on the calculated amount of operation.
With the above arrangement, the amount of operation of the drag varying means for minimizing the drag estimated from the thrust and motion state of the flying machine, is calculated, and the drag varying means is operated based on the calculated amount of operation. Therefore, the drag of the flying machine can be reduced effectively to enhance the energy efficiency, irrespective of the motion state of the flying machine.
To achieve the first object, according to a second aspect and feature of the present invention, there is provided a process for estimating the drag of a flying machine flying in the air, comprising
a first step of estimating a thrust T of the flying machine,
a second step of detecting the motion state of the flying machine by detecting the following conditions:
xcfx86: the roll attitude angle (an Eulerian angle about an X axis);
xcex8: the pitch attitude angle (an Eulerian angle about a Y axis);
U: the speed in a direction of the X axis;
V: the speed in a direction of the Y axis;
W: the speed in a direction of the Z axis;
P: the roll angular speed (an angular speed about the X axis);
Q: the pitch angular speed (an angular speed about the Y axis);
R: the yaw angular speed (an angular speed about the Z axis);
xcex1: the pitch angle formed by the direction of movement of the flying machine and the center angle of the flying machine,
a third step of calculating components Xa and Za of the air force in the directions of the X and Z axes applied to the flying machine by substituting the motion state detected at the second step into the following first equations:
Xa=mxc2x7(dU/dt+Qxc2x7Wxe2x88x92Rxc2x7V)+mxc2x7gxc2x7sin xcex8xe2x80x83xe2x80x83(1a)
Za=mxc2x7(dW/dt+Pxc2x7Vxe2x88x92Qxc2x7U)xe2x88x92mxc2x7gxc2x7cos xcex8xc2x7cos xcfx86xe2x80x83xe2x80x83(1b)
xe2x80x83wherein g is the gravitational acceleration, and m is the mass of the flying machine,
a fourth step of calculating the drag D of the flying machine by substituting the thrust T estimated at the first step, the pitch angle xcex1 detected at the second step and the components Xa and Za of the air force in the directions of the X and Z axes calculated at the third step into the following second equation:
D=(Txe2x88x92Xa)xc2x7cos xcex1xe2x88x92Zaxc2x7sin xcex1xe2x80x83xe2x80x83(2)
the third and fourth steps being carried out sequentially, after the first and second steps are carried out, irrespective of the order.
With the above arrangement, the thrust T of the flying machine is estimated at the first step, and the motion state of the flying machine including the pitch angle xcex1 is detected at the second step. The components of the air force in the directions of the X and Z axes applied to the flying machine, are calculated from the motion state at the third step, and the drag D of the flying machine is calculated from the thrust T, the pitch angle xcex1 and the components Xa, Za of the air force in the directions of the X and Z axes at the fourth step. Therefore, the drag D of the flying machine can be calculated precisely, irrespective of the motion state of the flying machine.
To achieve the second object, according to a third aspect and feature of the present invention, a boundary layer control system for controlling a boundary layer formed along the surface of a moving member is provided. The boundary layer control systems comprises a transition-point detecting means for detecting a transition point at which the boundary layer is transitioned from a laminar-flow boundary layer section to a turbulent-flow boundary layer section, a transition-point moving means for moving the position of the transition point along the surface of the moving member, and a control means for controlling the transition-point moving means, so that the distance from a front end of the moving member to the transition point is maximized.
With the above arrangement, the transition point, at which the boundary layer is transitioned from the laminar-flow boundary layer section to the turbulent-flow boundary layer section, is detected by the transition-point detecting means, and the transition-point moving means is controlled by the control means to maximize the distance from the front end of the moving member to the transition point. Therefore, the drag of the moving member can be reduced effectively, irrespective of the motion state of the moving member to enhance the energy efficiency. Particularly, the control is carried out, while directly monitoring that distance from the front end of the moving member to the transition point, which corresponds to the length of the laminar-flow boundary layer section where the drag is small. Therefore, it is possible to carry out a drag reducing control with extremely high accuracy.
To achieve the second object, according to a fourth aspect and feature of the present invention, there is provided a boundary layer control process for controlling the boundary layer formed along the surface of a moving member, comprising a first step of detecting a transition point at which the boundary layer is transitioned from a laminar-flow boundary layer section to a turbulent-flow boundary layer section, a second step of operating a transition-point moving means to move the position of the transition point rearwards, a third step of stopping the operation of the transition-point moving means, when the rearward movement of the transition point is stopped, and a fourth step of repeating the second and third steps, when the transition point starts to move.
With the above arrangement, the transition point, at which the boundary layer is transitioned from the laminar-flow boundary layer section to the turbulent-flow boundary layer section, is detected, and the transition-point moving means is operated so that the transition point assumes a rearmost position. Therefore, the drag of the moving member can be reduced, irrespective of the motion state of the moving member, thereby enhancing the energy efficiency. Particularly, the control is carried out, while directly monitoring the position of the transition point corresponding to the length of the laminar-flow boundary layer section where the drag is small and hence, the drag reducing control can be carried out with extremely high accuracy.